xref: /linux/security/integrity/evm/evm_main.c (revision db6d8d5fdf9537641c76ba7f32e02b4bcc600972)
1 /*
2  * Copyright (C) 2005-2010 IBM Corporation
3  *
4  * Author:
5  * Mimi Zohar <zohar@us.ibm.com>
6  * Kylene Hall <kjhall@us.ibm.com>
7  *
8  * This program is free software; you can redistribute it and/or modify
9  * it under the terms of the GNU General Public License as published by
10  * the Free Software Foundation, version 2 of the License.
11  *
12  * File: evm_main.c
13  *	implements evm_inode_setxattr, evm_inode_post_setxattr,
14  *	evm_inode_removexattr, and evm_verifyxattr
15  */
16 
17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
18 
19 #include <linux/module.h>
20 #include <linux/crypto.h>
21 #include <linux/audit.h>
22 #include <linux/xattr.h>
23 #include <linux/integrity.h>
24 #include <linux/evm.h>
25 #include <crypto/hash.h>
26 #include <crypto/algapi.h>
27 #include "evm.h"
28 
29 int evm_initialized;
30 
31 static char *integrity_status_msg[] = {
32 	"pass", "fail", "no_label", "no_xattrs", "unknown"
33 };
34 char *evm_hmac = "hmac(sha1)";
35 char *evm_hash = "sha1";
36 int evm_hmac_attrs;
37 
38 char *evm_config_xattrnames[] = {
39 #ifdef CONFIG_SECURITY_SELINUX
40 	XATTR_NAME_SELINUX,
41 #endif
42 #ifdef CONFIG_SECURITY_SMACK
43 	XATTR_NAME_SMACK,
44 #ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
45 	XATTR_NAME_SMACKEXEC,
46 	XATTR_NAME_SMACKTRANSMUTE,
47 	XATTR_NAME_SMACKMMAP,
48 #endif
49 #endif
50 #ifdef CONFIG_IMA_APPRAISE
51 	XATTR_NAME_IMA,
52 #endif
53 	XATTR_NAME_CAPS,
54 	NULL
55 };
56 
57 static int evm_fixmode;
58 static int __init evm_set_fixmode(char *str)
59 {
60 	if (strncmp(str, "fix", 3) == 0)
61 		evm_fixmode = 1;
62 	return 0;
63 }
64 __setup("evm=", evm_set_fixmode);
65 
66 static void __init evm_init_config(void)
67 {
68 #ifdef CONFIG_EVM_ATTR_FSUUID
69 	evm_hmac_attrs |= EVM_ATTR_FSUUID;
70 #endif
71 	pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
72 }
73 
74 static int evm_find_protected_xattrs(struct dentry *dentry)
75 {
76 	struct inode *inode = d_backing_inode(dentry);
77 	char **xattr;
78 	int error;
79 	int count = 0;
80 
81 	if (!(inode->i_opflags & IOP_XATTR))
82 		return -EOPNOTSUPP;
83 
84 	for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
85 		error = __vfs_getxattr(dentry, inode, *xattr, NULL, 0);
86 		if (error < 0) {
87 			if (error == -ENODATA)
88 				continue;
89 			return error;
90 		}
91 		count++;
92 	}
93 
94 	return count;
95 }
96 
97 /*
98  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
99  *
100  * Compute the HMAC on the dentry's protected set of extended attributes
101  * and compare it against the stored security.evm xattr.
102  *
103  * For performance:
104  * - use the previoulsy retrieved xattr value and length to calculate the
105  *   HMAC.)
106  * - cache the verification result in the iint, when available.
107  *
108  * Returns integrity status
109  */
110 static enum integrity_status evm_verify_hmac(struct dentry *dentry,
111 					     const char *xattr_name,
112 					     char *xattr_value,
113 					     size_t xattr_value_len,
114 					     struct integrity_iint_cache *iint)
115 {
116 	struct evm_ima_xattr_data *xattr_data = NULL;
117 	struct evm_ima_xattr_data calc;
118 	enum integrity_status evm_status = INTEGRITY_PASS;
119 	int rc, xattr_len;
120 
121 	if (iint && iint->evm_status == INTEGRITY_PASS)
122 		return iint->evm_status;
123 
124 	/* if status is not PASS, try to check again - against -ENOMEM */
125 
126 	/* first need to know the sig type */
127 	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
128 				GFP_NOFS);
129 	if (rc <= 0) {
130 		evm_status = INTEGRITY_FAIL;
131 		if (rc == -ENODATA) {
132 			rc = evm_find_protected_xattrs(dentry);
133 			if (rc > 0)
134 				evm_status = INTEGRITY_NOLABEL;
135 			else if (rc == 0)
136 				evm_status = INTEGRITY_NOXATTRS; /* new file */
137 		} else if (rc == -EOPNOTSUPP) {
138 			evm_status = INTEGRITY_UNKNOWN;
139 		}
140 		goto out;
141 	}
142 
143 	xattr_len = rc;
144 
145 	/* check value type */
146 	switch (xattr_data->type) {
147 	case EVM_XATTR_HMAC:
148 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
149 				   xattr_value_len, calc.digest);
150 		if (rc)
151 			break;
152 		rc = crypto_memneq(xattr_data->digest, calc.digest,
153 			    sizeof(calc.digest));
154 		if (rc)
155 			rc = -EINVAL;
156 		break;
157 	case EVM_IMA_XATTR_DIGSIG:
158 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
159 				xattr_value_len, calc.digest);
160 		if (rc)
161 			break;
162 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
163 					(const char *)xattr_data, xattr_len,
164 					calc.digest, sizeof(calc.digest));
165 		if (!rc) {
166 			/* Replace RSA with HMAC if not mounted readonly and
167 			 * not immutable
168 			 */
169 			if (!IS_RDONLY(d_backing_inode(dentry)) &&
170 			    !IS_IMMUTABLE(d_backing_inode(dentry)))
171 				evm_update_evmxattr(dentry, xattr_name,
172 						    xattr_value,
173 						    xattr_value_len);
174 		}
175 		break;
176 	default:
177 		rc = -EINVAL;
178 		break;
179 	}
180 
181 	if (rc)
182 		evm_status = (rc == -ENODATA) ?
183 				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
184 out:
185 	if (iint)
186 		iint->evm_status = evm_status;
187 	kfree(xattr_data);
188 	return evm_status;
189 }
190 
191 static int evm_protected_xattr(const char *req_xattr_name)
192 {
193 	char **xattrname;
194 	int namelen;
195 	int found = 0;
196 
197 	namelen = strlen(req_xattr_name);
198 	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
199 		if ((strlen(*xattrname) == namelen)
200 		    && (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
201 			found = 1;
202 			break;
203 		}
204 		if (strncmp(req_xattr_name,
205 			    *xattrname + XATTR_SECURITY_PREFIX_LEN,
206 			    strlen(req_xattr_name)) == 0) {
207 			found = 1;
208 			break;
209 		}
210 	}
211 	return found;
212 }
213 
214 /**
215  * evm_verifyxattr - verify the integrity of the requested xattr
216  * @dentry: object of the verify xattr
217  * @xattr_name: requested xattr
218  * @xattr_value: requested xattr value
219  * @xattr_value_len: requested xattr value length
220  *
221  * Calculate the HMAC for the given dentry and verify it against the stored
222  * security.evm xattr. For performance, use the xattr value and length
223  * previously retrieved to calculate the HMAC.
224  *
225  * Returns the xattr integrity status.
226  *
227  * This function requires the caller to lock the inode's i_mutex before it
228  * is executed.
229  */
230 enum integrity_status evm_verifyxattr(struct dentry *dentry,
231 				      const char *xattr_name,
232 				      void *xattr_value, size_t xattr_value_len,
233 				      struct integrity_iint_cache *iint)
234 {
235 	if (!evm_initialized || !evm_protected_xattr(xattr_name))
236 		return INTEGRITY_UNKNOWN;
237 
238 	if (!iint) {
239 		iint = integrity_iint_find(d_backing_inode(dentry));
240 		if (!iint)
241 			return INTEGRITY_UNKNOWN;
242 	}
243 	return evm_verify_hmac(dentry, xattr_name, xattr_value,
244 				 xattr_value_len, iint);
245 }
246 EXPORT_SYMBOL_GPL(evm_verifyxattr);
247 
248 /*
249  * evm_verify_current_integrity - verify the dentry's metadata integrity
250  * @dentry: pointer to the affected dentry
251  *
252  * Verify and return the dentry's metadata integrity. The exceptions are
253  * before EVM is initialized or in 'fix' mode.
254  */
255 static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
256 {
257 	struct inode *inode = d_backing_inode(dentry);
258 
259 	if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
260 		return 0;
261 	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
262 }
263 
264 /*
265  * evm_protect_xattr - protect the EVM extended attribute
266  *
267  * Prevent security.evm from being modified or removed without the
268  * necessary permissions or when the existing value is invalid.
269  *
270  * The posix xattr acls are 'system' prefixed, which normally would not
271  * affect security.evm.  An interesting side affect of writing posix xattr
272  * acls is their modifying of the i_mode, which is included in security.evm.
273  * For posix xattr acls only, permit security.evm, even if it currently
274  * doesn't exist, to be updated.
275  */
276 static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
277 			     const void *xattr_value, size_t xattr_value_len)
278 {
279 	enum integrity_status evm_status;
280 
281 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
282 		if (!capable(CAP_SYS_ADMIN))
283 			return -EPERM;
284 	} else if (!evm_protected_xattr(xattr_name)) {
285 		if (!posix_xattr_acl(xattr_name))
286 			return 0;
287 		evm_status = evm_verify_current_integrity(dentry);
288 		if ((evm_status == INTEGRITY_PASS) ||
289 		    (evm_status == INTEGRITY_NOXATTRS))
290 			return 0;
291 		goto out;
292 	}
293 	evm_status = evm_verify_current_integrity(dentry);
294 	if (evm_status == INTEGRITY_NOXATTRS) {
295 		struct integrity_iint_cache *iint;
296 
297 		iint = integrity_iint_find(d_backing_inode(dentry));
298 		if (iint && (iint->flags & IMA_NEW_FILE))
299 			return 0;
300 
301 		/* exception for pseudo filesystems */
302 		if (dentry->d_sb->s_magic == TMPFS_MAGIC
303 		    || dentry->d_sb->s_magic == SYSFS_MAGIC)
304 			return 0;
305 
306 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
307 				    dentry->d_inode, dentry->d_name.name,
308 				    "update_metadata",
309 				    integrity_status_msg[evm_status],
310 				    -EPERM, 0);
311 	}
312 out:
313 	if (evm_status != INTEGRITY_PASS)
314 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
315 				    dentry->d_name.name, "appraise_metadata",
316 				    integrity_status_msg[evm_status],
317 				    -EPERM, 0);
318 	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
319 }
320 
321 /**
322  * evm_inode_setxattr - protect the EVM extended attribute
323  * @dentry: pointer to the affected dentry
324  * @xattr_name: pointer to the affected extended attribute name
325  * @xattr_value: pointer to the new extended attribute value
326  * @xattr_value_len: pointer to the new extended attribute value length
327  *
328  * Before allowing the 'security.evm' protected xattr to be updated,
329  * verify the existing value is valid.  As only the kernel should have
330  * access to the EVM encrypted key needed to calculate the HMAC, prevent
331  * userspace from writing HMAC value.  Writing 'security.evm' requires
332  * requires CAP_SYS_ADMIN privileges.
333  */
334 int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
335 		       const void *xattr_value, size_t xattr_value_len)
336 {
337 	const struct evm_ima_xattr_data *xattr_data = xattr_value;
338 
339 	if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
340 		if (!xattr_value_len)
341 			return -EINVAL;
342 		if (xattr_data->type != EVM_IMA_XATTR_DIGSIG)
343 			return -EPERM;
344 	}
345 	return evm_protect_xattr(dentry, xattr_name, xattr_value,
346 				 xattr_value_len);
347 }
348 
349 /**
350  * evm_inode_removexattr - protect the EVM extended attribute
351  * @dentry: pointer to the affected dentry
352  * @xattr_name: pointer to the affected extended attribute name
353  *
354  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
355  * the current value is valid.
356  */
357 int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
358 {
359 	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
360 }
361 
362 static void evm_reset_status(struct inode *inode)
363 {
364 	struct integrity_iint_cache *iint;
365 
366 	iint = integrity_iint_find(inode);
367 	if (iint)
368 		iint->evm_status = INTEGRITY_UNKNOWN;
369 }
370 
371 /**
372  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
373  * @dentry: pointer to the affected dentry
374  * @xattr_name: pointer to the affected extended attribute name
375  * @xattr_value: pointer to the new extended attribute value
376  * @xattr_value_len: pointer to the new extended attribute value length
377  *
378  * Update the HMAC stored in 'security.evm' to reflect the change.
379  *
380  * No need to take the i_mutex lock here, as this function is called from
381  * __vfs_setxattr_noperm().  The caller of which has taken the inode's
382  * i_mutex lock.
383  */
384 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
385 			     const void *xattr_value, size_t xattr_value_len)
386 {
387 	if (!evm_initialized || (!evm_protected_xattr(xattr_name)
388 				 && !posix_xattr_acl(xattr_name)))
389 		return;
390 
391 	evm_reset_status(dentry->d_inode);
392 
393 	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
394 }
395 
396 /**
397  * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
398  * @dentry: pointer to the affected dentry
399  * @xattr_name: pointer to the affected extended attribute name
400  *
401  * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
402  *
403  * No need to take the i_mutex lock here, as this function is called from
404  * vfs_removexattr() which takes the i_mutex.
405  */
406 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
407 {
408 	if (!evm_initialized || !evm_protected_xattr(xattr_name))
409 		return;
410 
411 	evm_reset_status(dentry->d_inode);
412 
413 	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
414 }
415 
416 /**
417  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
418  * @dentry: pointer to the affected dentry
419  */
420 int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
421 {
422 	unsigned int ia_valid = attr->ia_valid;
423 	enum integrity_status evm_status;
424 
425 	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
426 		return 0;
427 	evm_status = evm_verify_current_integrity(dentry);
428 	if ((evm_status == INTEGRITY_PASS) ||
429 	    (evm_status == INTEGRITY_NOXATTRS))
430 		return 0;
431 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
432 			    dentry->d_name.name, "appraise_metadata",
433 			    integrity_status_msg[evm_status], -EPERM, 0);
434 	return -EPERM;
435 }
436 
437 /**
438  * evm_inode_post_setattr - update 'security.evm' after modifying metadata
439  * @dentry: pointer to the affected dentry
440  * @ia_valid: for the UID and GID status
441  *
442  * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
443  * changes.
444  *
445  * This function is called from notify_change(), which expects the caller
446  * to lock the inode's i_mutex.
447  */
448 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
449 {
450 	if (!evm_initialized)
451 		return;
452 
453 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
454 		evm_update_evmxattr(dentry, NULL, NULL, 0);
455 }
456 
457 /*
458  * evm_inode_init_security - initializes security.evm
459  */
460 int evm_inode_init_security(struct inode *inode,
461 				 const struct xattr *lsm_xattr,
462 				 struct xattr *evm_xattr)
463 {
464 	struct evm_ima_xattr_data *xattr_data;
465 	int rc;
466 
467 	if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
468 		return 0;
469 
470 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
471 	if (!xattr_data)
472 		return -ENOMEM;
473 
474 	xattr_data->type = EVM_XATTR_HMAC;
475 	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
476 	if (rc < 0)
477 		goto out;
478 
479 	evm_xattr->value = xattr_data;
480 	evm_xattr->value_len = sizeof(*xattr_data);
481 	evm_xattr->name = XATTR_EVM_SUFFIX;
482 	return 0;
483 out:
484 	kfree(xattr_data);
485 	return rc;
486 }
487 EXPORT_SYMBOL_GPL(evm_inode_init_security);
488 
489 #ifdef CONFIG_EVM_LOAD_X509
490 void __init evm_load_x509(void)
491 {
492 	int rc;
493 
494 	rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
495 	if (!rc)
496 		evm_initialized |= EVM_INIT_X509;
497 }
498 #endif
499 
500 static int __init init_evm(void)
501 {
502 	int error;
503 
504 	evm_init_config();
505 
506 	error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
507 	if (error)
508 		return error;
509 
510 	error = evm_init_secfs();
511 	if (error < 0) {
512 		pr_info("Error registering secfs\n");
513 		return error;
514 	}
515 
516 	return 0;
517 }
518 
519 /*
520  * evm_display_config - list the EVM protected security extended attributes
521  */
522 static int __init evm_display_config(void)
523 {
524 	char **xattrname;
525 
526 	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
527 		pr_info("%s\n", *xattrname);
528 	return 0;
529 }
530 
531 pure_initcall(evm_display_config);
532 late_initcall(init_evm);
533 
534 MODULE_DESCRIPTION("Extended Verification Module");
535 MODULE_LICENSE("GPL");
536